The invention relates to an apparatus for the continuous mixing of pulverulent substances with liquids, with a feed device for pulverulent substances, with a mixing chamber arranged below the feed device and into which projects from above a feed tube connected to the feed device, whilst a liquid suction tube issues tangentially into the upper area of the mixing chamber, whose lower area also contains at least one pump impeller, through which a radially outwardly directed conveying action is brought about, with a fixed screen surrounding the pump impeller along its outer circumferential surface and with an outlet arranged in the lower area of the mixing chamber.
It has proved very problemmatical to bring difficultly decomposable thickeners and stabilizers such as CMC, guar flour, alginates, whey proteins, pectin and other hydrocolloids, as well as difficultly dispersible substances such as aerosil, carboxypolymethylene, polyelectrolytes and carbon black into a colloidal solution or dispersion or suspension and this has not hitherto been satisfactorily solved.
Attempts have already been made to process in a batchwise manner with a dispersing apparatus able to produce shear forces difficultly wettable and/or scarcely dispersible substances. However, the main disadvantage of this procedure is that there is no controlled and clearly defined passage sequence of the dry product through the dispersing apparatus. In fact, certain powder fractions pass more frequently through the dispersing head than others and are consequently structurally processed to a greater extent and are also crushed. However, other powder fractions do not pass through the dispersing head or pass through it less often, so that these fractions are either not processed, or are inadequately processed. This leads to the disadvantage that the inadequately processed powder fractions are not decomposed or are only decomposed to a limited extent and are consequently not effective. Thus, the product structure is non-uniform and non-homogeneous, so that reproducible results are virtually unobtainable.
Attempts have also already been made to bring difficultly wettable and/or dispersible substances into contact with the liquid phase in batchwise manner, using a mixing or stirring apparatus. However, the substances are inadequately wetted, so that lumps and agglomerates form. It is therefore necessary to ensure that the substances are subsequently colloidally decomposed and deagglomerated with the aid of an in-line dispersing apparatus. Although the forced passage through the dispersing mechanism leads to a satisfactorily dispersed product, the overall structure of the charge is still not homogeneous. This is due to the fact that the single-pass apparatus is charged with a non-uniform product concentration, in which lumps and agglomerates can occur and must consequently be discharged by the same in an equally non-uniformly concentrated manner. In order to achieve a homogeneous charge, it is necessary to repeat the dispersing process and to displace the charge in circuit form over a container, in which a jet mixer is required to bring about a uniform suspension.
However, after being circulated several times, there is a serious risk of the mechanical overstressing of the solution/dispersion/suspension. However, in the case of thickeners and stabilizers, this known procedure leads to the shattering of the molecular chain, and the viscosity and consequently the combining power are reduced.
Another procedure has mainly been tried out with thickeners, in that the dry substances are introduced into the liquid phase by means of an injector. However, this procedure cannot be used if high concentrations are required or not easily flowing powders are used. However, an injector does not lead to colloidal decomposition of a single particle and at the most brings about a wetting of the primary particle agglomerates.
According to the prior art, a certain improvement is achieved with a construction in which regulatable quantities of dry substances are fed from a powder funnel into a dissolving chamber, where the dry substances are necessarily brought together with the quantitatively regulatable liquid phase. However, this known method, which also permits high concentrations in the in-line process, suffers from the disadvantage that the dry phase cannot be satisfactorily decomposed. This procedure also does not make it possible to bring about a satisfactory dispersing action.